BR112019021190B1 - PNEUMATIC WITH OPTIMIZED TOP AND TREAD - Google Patents

Abstract

The invention aims at increasing the resistance of tires comprising reinforcing reinforcement (5) and two crossed working layers (41, 42), whose breaking strength RC of each working layer (41, 42) is at least equal to 30000 N/dm. The working layers comprise reinforcing elements made up of single metallic strands or monofilaments having a section at least equal to 0.20 mm and at most equal to 0.5 mm. The density of reinforcing elements of each working layer is at least equal to 100 threads per dm and at most equal to 200 threads per dm. The tire also comprises axially outer cutouts (25). At least one of the two axially outer portions of the tread comprises a rubber material having a Shore hardness at least equal to 48 and at most equal to 60.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a passenger vehicle tire and more especially to the top of such a tire.

[0002] A tire having a geometry of revolution with respect to an axis of rotation, the geometry of the tire is generally described in a meridian plane that contains the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively designate the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane.

[0003] In the sequence, the expressions “radially interior to” and “radially exterior to” mean, respectively, “closer to the axis of rotation of the tire, according to the radial direction, than” and “farther away from the axis of rotation of the tire , according to the radial direction, that”. The expressions “axially interior to” and “axially exterior to” mean respectively closer to the equatorial plane, according to the axial direction, than” and “farther from the equatorial plane, according to the axial direction, than”. A "radial distance" is a distance from the tire's axis of rotation, and an "axial distance" is a distance from the equatorial plane of the tire. A “radial thickness” is measured according to the radial direction, and an “axial width” is measured according to the axial direction.

[0004] A tire comprises a top comprising a tread intended to come into contact with the ground through a tread surface, two beads intended to come into contact with a rim and two flanks which connect the top to the beads. On the other hand, a tire comprises a carcass reinforcement comprising at least one carcass layer, radially inside the top and connecting the two beads.

[0005] The tread of a tire is delimited, according to the radial direction, by two circumferential surfaces of which the radially outermost is called the tread surface and of which the radially innermost is called the bottom surface of sculpture. Furthermore, the tread of a tire is delimited, according to the axial direction, by two lateral surfaces. The tread, on the other hand, is made up of one or more rubber mixtures. The expression "rubber blend" designates a rubber composition comprising at least one elastomer and a filler.

[0006] The top comprises at least one top reinforcement radially inner to the tread. The top reinforcement comprises at least one working reinforcement, which comprises at least one working layer composed of reinforcing elements parallel to each other and forming, with the circumferential direction, an angle comprised between 15° and 50°. The top reinforcement can also comprise at least one reinforcement layer composed of reinforcement elements that form, with the circumferential direction, an angle comprised between 0 and 10°, the reinforcement reinforcement being in most cases, but not necessarily radially outside the working layers.

[0007] In order to obtain performance in grip on wet ground, cutouts are arranged in the tread. An indent designates either a well, or a groove, or an incision, or a circumferential groove and forms a space that opens onto the tread surface. A well has no main characteristic dimension on the tread surface. An incision or a groove has, on the road surface, two main characteristic dimensions: a width W and a length Lo, such that the length Lo is at least equal to 2 times its width W. An incision or a groove is therefore delimited by at least two main side faces that determine its length Lo and which are joined by a bottom face, the two main side faces being distant from each other by a non-zero distance, said width W of the incision or groove.

[0008] By definition, an incision or groove that is delimited by: • only two main lateral faces, is said to be transpassing, • by three lateral faces, of which two main ones determine the length of the cut, is called one-eyed, • by four side faces, of which the two main ones that determine the length of the cutout are said to be blind.

[0009] The difference between an incision and a groove is the value taken by the average distance that separates the two main side faces of the cutout, namely its width W. In the case of an incision, this distance is appropriate to allow the placing in contact of the two main side faces confronting each other when the incision was made in contact with the floor. In the case of a groove, the main side faces of that groove cannot come into contact with each other under normal running conditions. This distance to an incision is generally 1 millimeter (mm) for passenger vehicle tires. A circumferential groove is a substantially continuous, substantially circumferential direction indentation running the entire circumference of the tire.

[0010] More precisely, the width W is the average distance, determined in the length of the cutout and in a radial portion of the cutout comprised between a first circumferential surface, radially interior to the tread surface a radial distance of 1 mm, and a second surface circumferential, radially outside the bottom surface at a radial distance of 1 mm, in order to avoid any measurement problem linked to the connection of the two main side faces with the tread surface and the bottom surface.

[0011] The depth of the cutout is the maximum radial distance between the running surface and the bottom of the cutout. The maximum value of the cutout depths is called the carving depth D. The bottom carving surface is defined as the surface subjected to a radially inward translation of the tread surface by a radial distance equal to the carving depth.

STATE OF THE TECHNIQUE

[0012] In the current context of sustainable development, saving resources and, therefore, raw materials is one of the major objectives of industrialists. For passenger vehicle tires, one of the research avenues for this purpose consists in replacing the metallic cables usually used as reinforcement elements of different layers of the top reinforcement by single wires or monofilaments such as described in EP 0043563 in which this type of reinforcement elements is used with a double objective of mass gain and rolling resistance.

[0013] However, the use of this type of reinforcement elements has the drawback of causing a problem of buckling in compression that brings insufficient resistance to the tire, as described in document EP2537686. As this same document describes, the professional proposes a special arrangement of the different layers of the top reinforcement, a specific quality of the materials that make up the reinforcement elements of the top reinforcement to solve this problem.

[0014] A fine analysis of the physical phenomenon shows that the buckling of the monofilaments occurs in the most axially outer parts of the tread under the cutouts, as mentioned in document JP 2012071791, PCT/EP2016/075729, PCT/EP2016/075721, PCT/ EP2016/075725, PCT/EP2016/075741. This area of the tire has the particularity of being subjected to high compression efforts in the curved trajectories of the vehicle. The resistance to buckling of the monofilaments depends on the geometry of the cutouts, which thus shows the surprising influence of the sculpture on the resistance of the monofilaments.

DESCRIPTION OF THE INVENTION

[0015] The main objective of the present invention is therefore to increase the resistance of a tire whose reinforcing elements of the working layers are composed of monofilaments by designing an adapted tread.

[0016] This objective is achieved by a passenger vehicle tire, comprising: • a tread intended to come into contact with a ground through a tread surface and having an axial width LT, • the tread tread comprising two axially outer portions each having an axial width at most equal to 0.3 times the axial width LT, comprising at least one rubber material M intended to be in contact with the ground during the tread, • at least one axially outer portion comprising axially outer cutouts, an axially outer cutout forming a space that opens onto the tread surface and being delimited by at least two so-called main side faces connected by a bottom face, • the axially outer cutouts having a depth D defined by the maximum radial distance between the tread surface and the bottom face, • the tire comprising on the other hand a top reinforcement radially inside the tread, • the top reinforcement comprising a working reinforcement and a reinforcement, • the working reinforcement consisting of 2 working layers, each comprising reinforcing elements coated with an elastomeric material, parallel to each other and forming, respectively, with a circumferential direction (XX') of the tire, an oriented angle (A1, A2) at least equal to 20° and at most equal to 50° in absolute value and of opposite sign from one layer to the next, • the said reinforcement elements of each ply being made up of unitary metallic threads or monofilaments that have a section of which the smallest dimension is at least equal to 0.20 mm and at most equal to 0.5 mm, a breaking strength Rm, • the density of the reinforcing elements of each working layer being at least equal to 100 threads per dm and a maximum equal to 200 threads per dm, • the reinforcing armor comprising at least one reinforcing layer comprising reinforcing elements, parallel to each other and forming, with the circumferential direction (XX') of the tire, an angle B at most equal to 10° in absolute value, • the breaking strength Rc of each working layer is at least equal to 30 000 N/dm, Rc being defined by: Rc = Rm*S*d, where Rm is the tensile strength of the monofilaments in MPa, S is the section of the monofilaments in mm2 and d is the monofilament density of the working layer considered, in number of monofilaments per dm, • in at least one of the two axially outer portions (LS1, LS2 ), the at least one rubber material M intended to be in contact with the ground, has a Shore hardness at least equal to 48 and at most equal to 60.

[0017] Usually, the main side faces have substantially the same shape and are spaced apart from each other by a distance equal to the width W of the cutout. The greater the width W of the cutouts of the axially outer portions, the more the monofilaments are sensitive to buckling, yet the invention improves the resistance of the tire monofilaments whatever the width of the cutouts.

[0018] From the point of view of mechanical functioning, the buckling of a reinforcement element occurs in compression. It only occurs in the part of the working layers radially inside the portions that are the most axially outer of the tread since it is in this area that the compressive stresses are greatest in the case of transverse stress. Those portions that are the most axially outer have each of them a maximum axial width of 0.3 times the total width of the tread of the tyre.

[0019] Buckling is a complex and unstable phenomenon that leads to a failure due to fatigue of an object that has at least one dimension of an order of magnitude smaller than a main dimension such as beams or casings. Monofilaments are objects of this type with a section much smaller than their length. The phenomenon begins with a compression of the main dimension. It continues due to a dissymmetry of the monofilament geometry, or the existence of a transverse effort by placing the monofilament in flexion, a very destructive request for metallic materials. This complex phenomenon is notably quite dependent on boundary conditions, element mobility, direction of applied stress and deformation resulting from this stress. If this deformation is not carried out substantially in the direction of the principal dimension of the monofilament then buckling will not occur and, in the case of monofilaments surrounded by a rubber mixture matrix such as those in the working layers of a tyre, the stress is resumed by shearing the rubber mixture between the monofilaments.

[0020] Furthermore, the buckling of the monofilaments of the working layers only occurs in the most flexible portions of the tread. These portions may correspond to axially outer portions of the tread which comprise axially outer cutouts.

[0021] For non-axis outer cutouts, the compressive stress in the case of transverse stress on the tire is too small to cause buckling.

[0022] The axially outer cutouts can have any shape, curved, sinusoidal, zigzag, and thus allow or not, due to an adapted design, the relative displacements of their main lateral faces during rolling. To prevent a relative displacement of the main side faces of a cutout, it may be enough to create a sculpture element such that one of the faces will come to rest on the other when the considered displacement occurs. Cutouts of small width, or zigzag cuts, or sinusoidal cuts along the length of the cut, if the two main side faces are designed to rest on top of each other, are examples of this type of cutouts. If the undulation of the incision is depthwise, the relative radial offsets of the main lateral faces are blocked. If the incision presents a double undulation in the direction of its length and according to the depth, in this case the two movements will be blocked. As it is a large deformation of the top that causes the buckling of the monofilaments of the working layers and notably those allowed by the sculpture, any blockage of displacement in the sculpture can bring about an improvement in the resistance performance of the monofilaments.

[0023] All these cutout design parameters have restrictions and disadvantages such as: • the price of tire baking molds directly linked to the complexity of the mold elements that generate the complex cutouts, zigzag, or sinusoidal, called lamellae. • The difficulty in removing the mold from the mold for cutouts whose undulation is in the depth direction and tends to retain the mold lamellae. This geometry can create local tearing of the tread and make the tire unsaleable.

[0024] It is therefore interesting to find other parameters other than the design of the geometry of the cutouts to increase the resistance of the tire to buckling. On the other hand, even using all these cutting geometries for this purpose, for tires that are heavily used or made very light to reduce their raw material costs or improve their rolling resistance, it is interesting to be able to improve the resistance to buckling of the monofilaments by another design parameter.

[0025] To achieve these objectives, surprisingly, it is interesting to use, in one of the two axially outer portions (LS1, LS2), preferably the most stressed part of the tread, as material intended to be in contact with the ground a rubber material of low rigidity, namely that its Shore hardness, measured in accordance with ASTM 2240 or DIN 53505, is at least equal to 48 and at most equal to 60. A material intended to be in contact with the ground is a tread material in contact with the ground in the new state or in the worn state of the tire but in normal use on a vehicle, under legal and safe tire wear conditions.

[0026] According to the invention, one of the two outer portions (LS1, LS2) or both of the tread may comprise such a material and other rubber materials that have other mechanical properties in specific portions of the tread for purposes - for example - to improve localized wear or resistance of the tread. According to the invention, the entire tread could be made of this rubber material, even if only for the purpose of lowering the manufacturing cost.

[0027] The two axially outer portions of the tread may eventually contain one or more circumferential grooves to reduce the risk of aquaplaning on wet ground. For touring tires, these circumferential grooves generally represent a small width of contact area and have no known impact on monofilament buckling.

[0028] The monofilaments can have any section shape, knowing that the oblong sections represent an advantage over the circular sections of the same smaller dimension because their flexural inertia and, therefore, their resistance to buckling are higher. For a circular section, the smallest dimension corresponds to the diameter of the section. In order to guarantee resistance to fatigue rupture of the monofilaments and the shear resistance of the rubber mixtures located between the filaments, the density of reinforcing elements of each working layer is at least equal to 100 threads per dm and at most equal to 200 wires by dm. By density is meant the average number of monofilaments in a working layer width of 10 cm, this width being taken perpendicular to the direction of the monofilaments of the working layer considered. The distance between consecutive reinforcement elements can be fixed or variable. The placement of reinforcement elements during manufacture can be carried out by layer, by small strips or individually.

[0029] On the other hand, the resistance to buckling of a monofilament also depends on the resistance of the adjacent filaments, a beginning of buckling that can thus lead to another due to the effect of a distribution of the load around the monofilament that is subjected to buckling. In order to obtain an improved resistance performance, it is convenient not only to observe conditions of diameters and density of the monofilaments, but also to fulfill a condition that has as objective the resistance of the working layer, namely the resistance to rupture Rc of each working layer that must be be at least equal to 30 000 N/dm, Rc being defined by Rc = Rm*S*d, where Rm is the tensile strength of the monofilaments in MPa, S the section of the monofilaments in mm2 and d the monofilament density of the layer of work considered, in number of monofilaments per dm.

[0030] For a tire for which no mounting direction is imposed, a solution is to apply the invention to the two most axially outer portions of the tread.

[0031] For a tire for which an assembly direction is imposed, one possibility is to only apply the invention to the most axially outer portion of the tread, located on the outer side of the vehicle.

[0032] The carvings of the treads of passenger vehicle tires are usually either substantially symmetrical, or substantially antisymmetrical, or substantially asymmetrical.

[0033] A tread rubber material M, intended to be in contact with the ground, flexible, namely such that its Shore hardness is at least equal to 48 and at most equal to 60, is often penalized in performance of wear due to its flexibility. However, such a flexible rubber material is possibly characterized by low hysteresis, namely it has a dynamic property tan(d)max measured at 23°C of at least equal to 0.12 and at most equal to 0.30.

[0034] The dynamic property tan(δ)max is measured in a viscosity analyzer (Metravib VA4000), according to ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical specimen of 4 mm thickness and 400 mm2 section) is recorded, submitted to a sinusoidal request in alternating simple shear, at a frequency of 10 Hz, at 23°C. A sweep is performed in strain amplitude from 0% to 50% (outward cycle), and then from 50% to 0% (return cycle). For the back cycle, the maximum observed value of tan(δ) tan(δ)max is measured. The smaller the value of tan(δ), the better the tire's rolling resistance.

[0035] This characteristic associated with a suitable sculpture can bring an improvement in rolling resistance. As the use of monofilaments is aimed at gaining mass and improving rolling resistance, it is advantageous to use rubber materials that have this hysteretic property for the invention.

[0036] It is advantageous for an axially outer cutout to open axially outside an axially outer portion of the tread in order to be able to evacuate the water stored inside the cutout to the outside of the contact area when driving on a wet road.

[0037] Preferably, when the tread comprises at least one circumferential groove, an axially outer cutout opens axially into a circumferential groove of the tread band in order to be able to evacuate the water stored within the cutout to the main storage means water when driving on a wet road.

[0038] It is advantageous for grip that at least one of the axially outer portions of the tread has cutouts whose depth is close to the thickness of the tread in order to guarantee the grip performances of the tire once it is worn , namely cutouts with a depth D at least equal to 5 mm and spaced, in accordance with the circumferential direction (XX') of the tire, by a circumferential pitch P at least equal to 4 mm. The circumferential pitch is the mean circumferential distance on the considered most axially outer portions of the tread between the mean linear profiles of two consecutive circumferentially outer axially indentations. Usually, the treads of tires can have variable circumferential pitches, notably to limit noise during running-in.

[0039] For grip performance, it is also preferred that the axially outer cutouts are spaced, according to the circumferential direction (XX') of the tire, of a circumferential pitch P at the most equal to 50 mm, in order to avoid a density of the cutouts too small which leads to inadequate adhesion performance.

[0040] A preferred solution is for an axially outer cutout to be bridged. A gum bridge in an indentation corresponds to a local decrease in the depth of that indentation. This solution allows you to limit the relative displacements of the main side faces in all directions. They have, on the other hand, the disadvantage of preventing the laying on the plane and therefore impairing rolling resistance and of preventing the circulation of water at the bottom of the cutout. To facilitate flat laying and thus improve rolling resistance, the gum bridges may comprise an incision.

[0041] Preferably the depth D of the axially outer cutouts is at most equal to 8 mm to avoid too great a flexibility of the sculpture and loss of performance in terms of wear and tear resistance.

[0042] It is especially advantageous that the radial distance D1 between the bottom face of the axially outer cutouts and the top reinforcement is at least equal to 1 mm. In fact, this minimal amount of rubber materials allows you to protect the top from aggression and punctures by obstacles, pebbles, any fragments found on the ground.

[0043] It is preferred that the radial distance D1 between the bottom face of the axially outer cutouts and the top reinforcement is at most equal to 3.5 mm to obtain a high-performance tire in terms of rolling resistance.

[0044] A preferred solution, notably for noise performance, is that all axially outer cutouts are notches.

[0045] Advantageously the two axially outer portions of the tread band each have an axial width (LS1, LS2) at most equal to 0.2 times the axial width LT of the tread band.

[0046] Preferably, each working layer comprises reinforcing elements made up of unitary metal wires or monofilaments having a section whose smallest dimension is at least equal to 0.3 mm and at most equal to 0.37 mm, which constitute an optimum for the balance of the targeted performances: mass gain and resistance to buckling of the reinforcement elements of the working layers.

[0047] A preferred solution is for each working layer to comprise reinforcing elements that form, with the circumferential direction (XX') of the tire, an angle at least equal to 22° and at most equal to 35°, which constitutes an optimal compromise between the behavior and resistance performances of the tyre.

[0048] It is advantageous that the density of reinforcing elements of each working layer is at least equal to 120 threads per dm and at most equal to 180 threads per dm in order to guarantee the resistance of rubber mixtures working in shear between the reinforcement elements and the resistance of the latter in tension and compression.

[0049] The reinforcement elements of the working layers can be straight or not. They can be preformed, sinusoidal, zigzag, wavy or spiral shaped. The reinforcing elements of the working layers are made of steel, preferably made of carbon steel such as those used in steel cords; but it is of course possible to use other steels, for example stainless steels, or other alloys.

[0050] When a carbon steel is used, its carbon content (% by weight of steel) is preferably comprised within a range of 0.8% to 1.2%. The invention applies in particular to steel cord type steels of very high resistance (called "SHT" for "Super High Tensile"), ultra high resistance (called "UHT" for "Ultra High Tensile" or "MT" for "Mega Tensile”). Reinforcements made of carbon steel in that case have a tensile strength (Rm) which is preferably greater than 3000 MPa, more preferably greater than 3500 MPa. The total elongation at break (At) thereof, the sum of the elastic elongation and the plastic elongation, is preferably greater than 2.0%.

[0051] For reinforcements made of steel, measurements of breaking strength noted Rm (in MPa) and elongation at break noted At (total elongation in %) are carried out in tension in accordance with ISO 6892 from 1984.

[0052] The steel used, which is in particular carbon steel or stainless steel, can itself be coated with a metallic layer that improves, for example, the execution properties of the steel monofilament, or the use properties of the reinforcement and/or the tire itself, such as adhesion properties, corrosion resistance or even aging resistance. According to a preferred embodiment, the steel used is covered with a layer of brass (Zn-Cu alloy) or zinc; it is remembered that during the wire manufacturing process, the brass or zinc coating facilitates the drawing of the wire, as well as the bonding of the wire with the rubber. But the reinforcements could be covered with a thin metallic layer other than brass or zinc, which has the function, for example, to improve the corrosion resistance of these wires and/or their adhesion to rubber, for example a thin layer of Co, Ni , Al, from an alloy of two or more of the compounds Cu, Zn, Al, Ni, Co, Sn.

[0053] Preferably, the reinforcing elements of the at least one reinforcing layer are made of fabric of the type aliphatic polyamide, aromatic polyamide, combination of aliphatic polyamide and aromatic polyamide, polyethylene terephthalate or rayon since the textile materials are specially adapted to this type of use due to their low mass and high rigidity. The distance between consecutive reinforcement elements of the reinforcement layer can be fixed or variable. The placement of reinforcement elements during manufacture can be carried out by layer, by small strip or individually.

[0054] It is advantageous that the reinforcement reinforcement is radially outside the work reinforcement for a good duration of the latter in resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The characteristics and other advantages of the invention will be better understood with the help of figures 1 to 3, said figures not being represented to scale but in a simplified way, in order to facilitate the understanding of the invention: - Figure 1 is a perspective view representing a tire part according to the invention, in particular its architecture and its tread. - Figure 2 represents the meridian section of the top and illustrates the axially outer parts 22 and 23 of the tread, as well as their width. - Figures 3A and 3B show two types of radially outer meridian profiles of the tread of a touring tyre.

DETAILED DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 represents a part of the top of a tire. The tire comprises a tread 2 intended to come into contact with a ground via a tread surface 21. In the axially outer portions 22 and 23 of the tread, grooves 26 are arranged, axially outer cutouts between which incisions 24 s grooves 25. The tire furthermore comprises a top reinforcement 3 comprising a working reinforcement 4 and a reinforcing reinforcement 5, the working reinforcement comprising 2 working layers 41 and 42. Figure 1 on the other hand represents cutouts blind, one-eyed, externally or internally passing through axially simple and complex, namely with parallel lateral faces or with lateral faces with zigzag or sinusoidal portions in the main direction of the cut or in its depth in order to block certain relative displacements of the 2 lateral faces.

[0057] Figure 1 represents in the axially outer parts 22 and 23 of the tread band, only axially outer axial grooves, according to the axial axis (YY'). In reality, this representation is of pure convenience for the readability of figure 1, the axially outer grooves in the treads of passenger cars may, depending on the intended performance, notably in grip on wet ground, form an angle with the axial direction ( YY') between plus or minus 60°.

[0058] Figure 2 schematically represents the meridian section of the top of the tire according to the invention. It especially illustrates the widths LS1 and LS2 of the axially outer portions 22 and 23 of the tread, as well as the total tread width of the tire LT. Also represented are the depth D of an axially external cutout 24, 25 and the distance D1 between the bottom face 243 of an axially outside cutout 24 and the top reinforcement 3 measured in a meridian section of the tire. A tire meridian section is obtained by cutting the tire according to two meridian planes. By way of example, a meridian cut of a tire has a thickness according to the circumferential direction of about 60 mm at the level of the tread. The measurement is carried out keeping the distance between the two beads identical to that of the tire mounted on its rim and slightly inflated.

[0059] In figures 3A and 3B, the axial edges 7 of the tread are determined, which allow measuring the width of the tread. In figure 3A in which the tread surface 21 is secant with the outer axial surface of the tire 8, the axial edge 7 is trivially determined by the professional. In figure 3B, in which the tread surface 21 is continuous with the outer axial surface of the tire 8, the tangent to the tread surface at any point of said tread surface within the transition zone is drawn in a meridian section of the tyre. towards the flank. The first axial edge 7 is the point at which the angle β between said tangent and an axial direction YY' is equal to 30°. When there are several points for which the angle J between said tangent and an axial direction is equal to 30°, the point which is radially the outermost is chosen. The same procedure will be used to determine the second axial edge of the tread.

[0060] The inventors performed calculations based on the invention for a tire of size 205/55 R16, inflated to a pressure of 2 bars, comprising two working layers comprising monofilaments made of steel, with a diameter of 0.3 mm, distributed according to a density of 158 threads per dm and which form, with the circumferential direction XX', angles equal to 25° and -25° respectively. The monofilaments have a breaking strength Rm equal to 3500 MPa and the working layers each have a breaking strength Rc equal to 39 000 N/dm. The tire comprises axially outer cutouts in the two axially outer tread portions of the tire having an axial width equal to 0.21 times the axial width of the tread. The radial distance D1 between the bottom face of the axially outer cutouts and the top reinforcement is at least equal to 2 mm.

[0061] Different tires were calculated. Tire A, which does not embody the invention, comprises grooves with a width equal to 5 mm and a depth equal to 6.5 mm. The rubber material of the two axially outer portions of the tread of that tire A which does not embody the invention, intended to be in contact with the ground during the running-in, is a material characterized by its high stiffness in order to obtain a good wear compromise. and behavior. The properties of this rubber material are a Shore hardness of 67 and a tan(δ)max of 0.35.

[0062] Tire B, according to the invention, is identical in all points to tire A, except for the fact that the rubber material of the two outer portions of the tread of that tire B according to the invention, intended for being in contact with the ground when running in, it is a material characterized by its low rigidity: The properties of this rubber material are a Shore hardness equal to 52 and a tan(δ)max equal to 0.17.

[0063] The calculation conditions reproduce the running conditions of a front tire on the outer side of the curve, that is to say the one that is most used in a touring vehicle. Two situations were modeled, which represent the conditions seen by the tire when the vehicle makes a curve under a lateral acceleration of 0.3 g and 0.7 g. At 0.3 g of transverse acceleration, the tire is subjected to a lateral force (Fy) of 150 daN and a vertical force (Fz) of 568 daN for an inclination of the wheel axis of 0.68°. At 0.7 g of transverse acceleration, the tire is subjected to a lateral force (Fy) of 424 daN and a vertical force (Fz) of 701 daN for a wheel axis inclination of 3°. The use, in tire B according to the invention, of a rubber material, in the two axially outer portions of the tread, intended to be in contact with the ground, makes it possible to reduce the magnitude of the stresses calculated in the most stressed monofilaments from 6 .5% for the two stress levels in relation to these same stresses calculated under the same stress conditions on tire A.

[0064] On the other hand, the gain in rolling resistance with the use of the tread material of tire B compared to tire A is at least equal to 15%.

Claims (10)

1. Tire (1) for a passenger vehicle, comprising: • a tread (2) intended to come into contact with a ground via a tread surface (21) and having an axial width LT, • the tread tread (2) comprising two axially outer portions (22, 23) each having an axial width (LS1, LS2) at most equal to 0.3 times the axial width LT, comprising at least one rubber material M intended to be in contact with the ground when running in, • at least an axially outer portion (22, 23) comprising axially outer cutouts (24, 25), an axially outer cutout (24, 25) forming a space that opens into the surface tread (21) and being delimited by at least two main side faces (241, 242) connected by a bottom face (243), • the axially outer cutouts (24, 25) having a depth D defined by the maximum radial distance between the tread surface (21) and the bottom face (243), • the tire additionally comprising a top reinforcement (3) radially inside the tread (2), • the top reinforcement (3) comprising a reinforcement of work (4) and a reinforcement reinforcement (5), • the work reinforcement (4) being constituted by two layers of work (41, 42) comprising, each one of them, reinforcement elements coated with an elastomeric material, parallel to each other themselves and which respectively form with a circumferential direction (XX') of the tire, an oriented angle (A1, A2) at least equal to 20° and at most equal to 50° in absolute value and of opposite sign from one layer to the next , • the said reinforcing elements of each ply being made up of unitary metallic threads or monofilaments having a section whose smallest dimension is at least equal to 0.20 mm and at most equal to 0.5 mm, a resistance to rupture Rm, • the density of the reinforcing elements of each working layer being at least equal to 100 threads per dm and at the most equal to 200 threads per dm, • the reinforcing armature (5) comprising at least one reinforcing layer comprising reinforcing elements, parallel to each other and forming, with the circumferential direction (XX') of the tire, an angle B at most equal to 10° in absolute value, the breaking strength Rc of each working layer (41, 42) is at least equal to 30 000 N/dm, Rc being defined by: Rc = Rm*S*d, where Rm is the tensile strength of the monofilaments in MPa, S is the section of the monofilaments in mm2 and d is the density of monofilaments of the working layer considered, in number of monofilaments per dm, characterized by the fact that in at least one of the two axially outer portions (LS1, LS2), the at least one rubber material M intended to be in contact with the ground at the time of running-in, has a Shore hardness at least equal to 48 and at most equal to 60. 2. Tire according to claim 1, characterized in that the rubber material M, in at least one of the two axially outer portions (LS1, LS2) and intended to come into contact with the ground during the running-in, has a dynamic property tan(d)max measured at 23°C at least equal to 0.12 and at most equal to 0.30. 3. Tire according to claim 1 or 2, characterized in that axially outer cutouts (24, 25) have a depth D at least equal to 5 mm and are spaced according to the circumferential direction (XX') of the pneumatic, of a circumferential pitch P at least equal to 4 mm. 4. Tire according to any one of claims 1 to 3, characterized in that the axially outer cutouts (24, 25) are spaced, according to the circumferential direction (XX') of the tire, of a circumferential pitch P in the maximum equal to 50 mm. 5. Tire according to any one of claims 1 to 4, characterized in that the depth D of the axially outer cutouts (24, 25) is at most equal to 8 mm. 6. Tire according to any one of claims 1 to 5, characterized in that the radial distance D1 between the bottom face (243) of the axially outer cutouts (24) and the top reinforcement (3) is at least equal to 1 mm. 7. Tire according to any one of claims 1 to 6, characterized in that the radial distance D1 between the bottom face (243) of the axially outer cutouts (24) and the top reinforcement (3) is at most equal to 3.5 mm. 8. Tire according to any one of claims 1 to 7, characterized in that the two axially outer portions (22, 23) of the tread (2) each have an axial width (LS1, LS2) maximum equal to 0.2 times the LT axial width. 9. Tire according to any one of claims 1 to 8, characterized in that each working layer (41, 42) comprises reinforcing elements made up of unitary metal wires or monofilaments having a diameter at least equal to 0.3 mm and at most equal to 0.37 mm. 10. Tire according to any one of claims 1 to 9, characterized in that each working layer (41, 42) comprises reinforcing elements, which form, with the circumferential direction (XX') of the tire, an angle ( A1, A2) at least equal to 22° and at most equal to 35°.

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